This invention relates to filtering apparatus.
In industrial and laboratory separation processes, particularly as part of an analytical procedure or in the biotechnological and pharmaceutical industries, it is often a necessary part of the purification procedure for any product to pass through one or more stages of filtration. Thus, an essential part of many processing activities is that of separating microparticles from a suspension. By "microparticle" is meant a particle of dimension no greater than about 50 microns with the term "particle" intended to include cells, viruses and macromolecules. The need for filtering systems is thus seen as an important tool in the extraction of products and by-products or in purification procedures.
Where the filtration system is primarily a barrier of fixed diameter pores, the effect is merely to prevent all microparticles larger than the maximum pore size from being transported by the carrier flow across the filter. As the residue builds up, the transport efficiency becomes worse because of pore blocking. Blocking cuts down flow and has the effect of progressively reducing the particle size transported, being eventually far smaller than the original pore diameter. Multi-stage filtration, using a series of filters with different pore sizes, alleviates the rapid loss common to single filters, but eventually requires replacement as with single units. Such methods are costly and in many circumstances impracticable.
Ideally, a filtration system should be programmable to a range of pore sizes and be able to clear fouling without disassembly. It is an object of this invention to provide approved filtering apparatus meeting these desiderata.
It should be recognised that, in a different field, U.S. Pat. No. 2,315,651 discloses an adjustable screen for a shaker assembly, the screen having top and bottom plates each with an array of square apertures. A screw thread arrangement is provided for sliding the top plate, to vary the registration of the top and bottom apertures. This is intended to reduce the time needed to adjust the equipment to meet varying sifting requirements.